In the field of semiconductor production, large quantities of chemical solutions and water are used in wet processes, and as molding materials for the pipeline inclusive of piping materials and joints for the transport of such liquors, fluororesins which are highly resistant to chemicals and heat are employed.
Among fluororesins, tetrafluoroethylene [TFE]-perfluoro(alkylvinylether) [PAVE] copolymers [PFA] are used universally and particularly TFE-perfluo(propylvinylether) [PPVE] copolymers having excellent chemical resistance and heat resistance as well as good stress-crack resistance are in popular use as appropriate molding materials. Although PFA has been found to be free from prominent drawbacks, its copolymers with the PPVE unit content confined to less than 3.5 mass % are used in many cases today for suppressing the cost increase and improving the efficiency of copolymer production.
In molding fluororesins, whereas geometrically uncomplicated parts such as tubing are produced by extrusion molding, geometrically complicated parts such as joints and other joints are chiefly produced by injection molding. For injection molding, fluororesins having comparatively low melt viscosities are used mainly for improved molding productivity, although these are inferior in stress-crack resistance to fluororesins having high melt viscosities. As the fluororesins for injection molding, taking PFA as an example, resins of the grade with a melt flow rate [MFR], which is an index of melt viscosity, of not less than 10 g/10 minute are broadly sold and used.
In the field of semiconductor production processes, studies have been undertaken on the use of ozone, which has a strong degrading effect on organic matter, in the cleaning of wafers and devices, for resist stripping, and for imparting hydrophilicity to surfaces, among other uses in the recent years.
Ozone has heretofore been used in the form of ozonized water for the purification and disinfection of town water but, for the following reasons, ozone crack resistance was not a major consideration.    1. Since the ozone concentration of ozonized water, even when high, is of the order of 200 ppm, the influence of ozone was limited.    2. In cases where the effect of trace metal contaminations of town water and the like flowing through pipelines can be disregarded, metallic piping has so far been used because it has nothing wrong with its strength.
However, in semiconductor production processes, where metal contaminations must be minimized, it is necessary to use resins as molding materials for piping materials and joints and, it is preferable to use fluororesins in view of their superior chemical resistance and heat resistance.
Furthermore, in the recent semiconductor production processes, for the purpose of improving the process efficiency, particularly in the resist stripping stage, several means have been proposed for enhancing the activity of ozone, such as increasing the ozone concentration of ozonized water from the order of 200 ppm to 1,000–200,000 ppm, increasing the treating temperature from the general room temperature to 80–150° C., and adding water vapor as a catalyst. As the conditions of use of ozone have thus become more and more tough, the load on the piping materials and chambers has been considerably increased. The problem accordingly developed that if the conventional PFA is used as the fluororesin, the ozone will penetrate into the moldings to cause cracks which inevitably lead to decreases in dynamic strength.
As a means for preventing ozone crack troubles, it was proposed to replace PFA with polytetrafluoroethylene [PTFE] which is more resistant to ozone but PTFE moldings are deficient in transparency so that when these are used as pipeline materials, the movement and level of the liquid in the pipeline cannot be clearly detected, resulting in lack of visibility. Furthermore, PTFE cannot be used for melt-molding, and in the case of producing geometrically complicated parts, the parts must be machined out of a block molding but this practice adds to increased industrial wastes and processing cost.
As the ozone-resistant fluororesin for injection molding, a PFA with a melting point of 300–310° C. is commercially available. However, this commercial resin is deficient in the folding endurance with the indicator MIT value being as few as 200,000 cycles and it is disclosed only that its ozone resistance is derived exclusively from the high purity of the fluororesin.